I . Classifying Rocks

1. Rocks are made of mixtures of minerals and other material.

2. Granite- is a rock made of a couple different minerals and materials.

Granite usually has a high silica content.

3. Basalt is a dark colored rock that has low silica content.

B. Texture

1. Grain size- often you can see grain in a rock without a microscope, but sometimes you need one;

easily to grain is coursed grain, hard to see: fine grain.

2. Grain shape- is usually different crystals can help determine what kind of grain it is,

if it’s smooth or jagged grain.

3. Grain patterns- some form in layers like sheets, and others swirl randomly this is called gness

C. How Rocks Form

1. Using color, texture, and mineral composition, geologist can classify a rock according to its origin.

2. Geologists classify rocks into three major groups:

Igneous rock, Sedimentary rock, and metamorphic rock.

a) Igneous rock- formed from cooling of magma or lava.

b) Sedimentary rock- forms when particles of other rocks or the remains of plants and

animals are pressed and cemented together, forms in layers below the surface.

c) Metamorphic rock- forms when existing rock is changed by heat,

pressure or chemical reaction, most is formed underground.